Imaging of a large field of view has many applications in the fields of defense, security, monitoring, entertainment, industry, medical imaging and many other fields. Imaging of a panoramic or nearly spherical field of view, using a single image-capturing device, is especially applicable for a variety of needs due to its relative simplicity, low-cost and miniaturization possibilities.
Security cameras often require the ability to view as large a field of view as possible to enable imaging of all occurrences in a scene for purposes of real-time surveillance and warning or for documentation and restoration of images at later stages.
Inner body imaging during diagnostic or therapeutic medical procedures requires real time viewing of a large field of view in order to provide the surgeon with the ability to orientate and maneuver the medical scope within the body without endangering body organs or risk causing damage to body tissue. These applications also require the ability to illuminate the scene that is imaged in order to provide a clear and understandable image to the physician.
Additional applications, which require a large field of view exist, include remote operation of ground vehicles, imaging equipment for reconnaissance and information gathering, viewing the interior of devices such as engines, and cinematic and home entertainment applications.
One of the prior art techniques of panoramic imaging makes use of several image capturing devices, each one aimed at a different sector limited in width, combined in a manner such that all of them together, when properly aligned, cover a full 360 degrees field of view. Another prior art method for panoramic imaging relies on a single image-capturing device, rotated around a vertical axis. In this method the image-capturing device covers a limited sector at any single moment; but, while completing a full rotation, it creates a sequence of images, which are combined together to form a panoramic image.
The main disadvantage of these prior art methods is their relative complexity. Some prior art methods make use of moving/rotating mechanisms, which require frequent alignment and very often turn out to be maintenance-intensive.
The ability to make use of a single imaging device, equipped with an optical structure, which would enable viewing of the entire perimeter around the imaging device, would be invaluable for the applications described hereinabove.
A prior art approach using a single imaging device makes use of axi-symmetric reflective surfaces to reflect a panoramic field of view towards a single image-capture device. In this approach a circular image is formed on the focal plane array of the image-capturing device. The shape of the image derives from the reflection of the surrounding field of view by the reflective lens, and often includes aberrations. The image shape and additional aberrations are corrected by image processing techniques. Such a prior art design is described in U.S. Pat. No. 6,028,719, in which a method for capturing a nearly spherical field of view using a single axi-symmetric reflective mirror with a hole in its center is described. The main disadvantages of the methods described in U.S. Pat. No. 6,028,719 include the relatively complex fabrication of the optical components to achieve high optical performance, the high fabrication costs of the imaging device and its sensitivity to environmental conditions. Furthermore, such devices provide relatively poor image quality.
A simpler, cheaper and more robust solution for imaging and/or illuminating a panoramic or nearly spherical filed of view would be to use an aspheric optical block, a single image capturing device and in some embodiments—an illumination source. Attempts to fabricate such a device have been made, e.g., in U.S. Pat. No. 6,341,044, which makes use of an optical block and a single image capturing device to provide panoramic imaging. The design used in U.S. Pat. No. 6,341,044 includes a spherical optical block having one refractive surface and one reflective surface. The spherical shape of the optical block and the existence of a single refractive surface incorporated within the optical block itself introduce aberrations that must be corrected by several sets of additional optical lenses along the optical path, as described extensively in the patent.
It is therefore an object of the present invention to provide an optical block designed to provide a reflection of a panoramic perimeter, having an acceptable level of distortions and aberrations.
It is another object of the present invention to provide an optical block designed to enable acquiring of a nearly spherical field of view.
It is another object of the present invention to provide an imaging assembly, based on the optical block of the invention.
It is yet another object of the present invention to provide a method of illuminating the scene that is imaged, simultaneously while imaging; utilizing the same optical block for both coverage of the scene and the transmittance of illumination to the scene.
Further purposes and advantages of this invention will appear as the description proceeds.